Our testing requirements for vibratory ground improvements using stone columns are being simplified. We have also begun to consider the acceptance of partial-depth Vibro treatment on a case-by-case basis.
Below, we detail the changes being made and how this could affect you.
Ground improvement enables sites with poor load-bearing capacity to be strengthened. This means that the loadings of the proposed building can be adequately supported off suitable foundations.
Vibro displacement using vibro stone columns is a method of enhancing ground bearing capacity and limiting settlement. Typical applications include the support of foundations, slabs, hard standings, pavements, tanks or embankments.
Soft soils can be reinforced to achieve improved specification requirements, whilst slopes can be treated to prevent slip failure and both natural soils and made ground can be improved.
Testing should be carried out across the full site and cover all of the various ground conditions to confirm that the ground improvement works meet the design criteria.
• Plate tests should also be carried out with 600mm diameter plates loaded to 3 times working load or 11 tonnes, whichever is greater.
• We require these tests to be carried out at a minimum rate of 1 test per rig per day.
• Dummy footing tests should also be carried out with 1500 x 600mm plates, loaded to at least 1.5 times working load (kN/m2) for a minimum period of 13 hours.
• We require these tests to be carried out at a minimum rate of 1 per week.
Penetration tests should be carried out:
• At a rate of 1 per 20-50 stone columns or 1 test for not more than 500m2, with a minimum of 1 test for each structural unit.
• Penetration tests won’t be required if dummy footing tests are carried out at the above rate.
Vibro treatment should be carried out in accordance with the ‘Institute of Civil Engineers: 1987 Specification for ground treatment: Notes for guidance’ and to a depth sufficient to reach an adequate bearing stratum.
The design and construction of vibro stone columns and foundations should be in accordance with the Premier Guarantee Technical Manual and recognised publications from British Standards, Eurocodes, CIRIA, BRE and ICE.
Every care was taken to ensure the information in this article was correct at the time of publication (November 2022). Guidance provided does not replace the reader’s professional judgement and any construction project should comply with the relevant Building Regulations or applicable technical standards. For the most up to date Premier Guarantee technical guidance please refer to your Risk Management Surveyor and the latest version of the Premier Guarantee Technical Manual.